Final answer:
Ice floats on liquid water because it is less dense than water due to the rigid lattice structure formed by hydrogen bonding. This allows fish and other organisms to survive under the ice. If ice were denser than water, bodies of water would freeze from the bottom up.
Step-by-step explanation:
Ice floats on liquid water because it is less dense than water. When water freezes, it forms a rigid lattice structure due to the hydrogen bonding between water molecules. This structure causes the molecules in solid ice to be spread out more, making it less dense than liquid water. If ice were denser than water, it would sink and freeze bodies of water from the bottom up, which would be harmful to aquatic life.